1. Field of the Invention
The present invention relates to a transmitter structure and, more particularly, to the transmitter structure of a portable electronic device, e.g., a portable telephone or a video camera, which is used outdoors and designed to reduce wind noise.
2. Description of the Prior Art
Various transmitter structures designed to reduce noise caused by user's breath and wind in outdoor use have been proposed.
For example, Japanese Unexamined Patent Publication No. 6-269084 discloses a technique of controlling the cutoff frequency of a high-pass filter for reducing wind noise by using a detection means for detecting wind on the basis of differential outputs from two microphones.
In another transmitter structure disclosed in Japanese Unexamined Patent Publication No. 7-202997, the sound hole formed in the case is connected to the microphone through a sound path to prevent breath from directly entering the microphone.
Since the above conventional transmitter structure has a filter for reducing wind noise and a wind detection circuit, a reduction in cost is difficult to attain.
In addition, since two microphones are used, it is difficult for this structure to realize a compact electronic device for which portability is required, in particular.
Furthermore, the structure having the sound path needs to weaken breath and wind in the sound path to reduce the amount of wind or the like reaching the microphone. For this reason, the width, height, and length of the wind path are respectively set to about 2.5 mm, 0.5 mm, and 25 mm. Especially the length must be set to 25 mm or more. This structure is not therefore suited for a reduction in size, either.
A pressure gradient microphone such as a directional or close-talking microphone is susceptible to the influence of wind, in particular, as compared with a non-directional microphone. It is therefore difficult to apply such a microphone to a portable telephone, a video camera, and the like which are used outdoors.